1. Field of the Invention
The present invention relates to a bearing device that includes a bearing portion and an oil supply unit provided adjacent to the bearing portion in the axial direction.
2. Description of the Related Art
In recent years, various types of machine tools are requested to increase the speed of a main spindle in order to improve the processing efficiency and the productivity. When the main spindle is rotated at a high speed, a defect such as a seizure tends to be caused at a bearing portion that supports the main spindle, and thus lubrication of the bearing portion is particularly important. Oil-air lubrication is known as a method of lubricating the bearing portion. In the oil-air lubrication, however, the amount of oil supplied to the bearing portion tends to be larger than necessary, which increases the stirring resistance due to lubricating oil during rotation of the bearing portion, causing a torque loss.
As disclosed in Japanese Patent Application Publication No. 2004-108388 (JP 2004-108388 A), for example, oil supply by an oil supply unit incorporated adjacent to a bearing portion in the axial direction has been proposed as a lubrication method that is different from the oil-air lubrication. The oil supply unit has a pump, and supplies lubricating oil to the bearing portion as oil droplets using the pump.
With the bearing device described in JP 2004-108388 A, the oil supply unit can supply lubricating oil to the bearing portion as necessary, which makes it possible to secure lubrication of the bearing portion. In such a bearing device, it is only necessary to control the amount of lubricating oil supplied from the oil supply unit. However, the method of controlling the oil supply amount is not specified, and has been left as an issue. Bearing devices that include the oil supply unit described above are applied not only to machine tools but also to a variety of other devices, and have a similar issue.
For bearing devices provided with a bearing portion and an oil supply unit, the inventors of the present invention focused on maintaining the rotation performance of the bearing portion with an oil supply amount that is as small as possible in order to reduce the stirring resistance due to lubricating oil, and achieved the present invention.